What did God mean when He said, "Be sure your sin will find you out" (Numbers 32:23)?

from the old testament

• After God led the Israelites out from Egypt, the goal was to take them straight into the promised land (Canaan) to take possession of it (Exodus 3:8). However, when they got close, Israel sent twelve men to spy out the land. Ten of them returned, and in a show of distrust of God, they expressed fear of the inhabitants, discouraging the Israelites from entering (Numbers 13:31–33). The only two who encouraged them to enter under God’s protection were Joshua and Caleb (Numbers 14:6–9).
• Because of their distrust in Him, God punished them with wandering in the desert until they all died (Numbers 14:29–34). Numbers 32 is the account of after they had all died. Once again, Israel was prepared to enter the land, but the tribes of Ruben and Gad saw that the land just outside Canaan was particularly good for their flocks (Numbers 32:1). They then asked Moses for permission to settle there (vv 2–5).
• Moses interpreted their request as similar to that of the first generation of spies and was angry at them (vv 8–13). He feared that if Ruben and Gad stayed behind, the rest of Israel would also be tempted not to enter Canaan, bringing God’s wrath a second time (Numbers 32:6–15).
• However, the leaders of Ruben and Gad reassured Moses that their intention was to only build the basic structures the women and children would need before setting out to join the rest of the Israelites in the battle for the promised land (Numbers 32:16–19).
• After that clarification, Moses agreed that they could eventually settle in Gilead (Numbers 32:20–22). However, he warned that if they did not do as they promised, “you have sinned against the LORD, and be sure your sin will find you out” (v 23).
• What Moses was saying was that if they sinned by not entering the land, their sin of not obeying would find them out in the sense that it would come with God’s punishing wrath. That is because, though Moses would die before seeing them enter the land (Numbers 20:12), God would see whether they did and expose their sin if they did not, judging them for it.

from the new testament

• The New Testament also teaches that no sin is hidden from God. Jesus told His disciples, "Nothing is covered up that will not be revealed, or hidden that will not be known (Luke 12:2).
• The writer of reaffirms that point: "And no creature is hidden from his sight, but all are naked and exposed to the eyes of him to whom we must give account" (Hebrews 4:13). Even with other people don't see, God sees.
• But our hope is in Christ. As Paul wrote to the Corinthians, "For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God" (2 Corinthians 5:21).

implications for today

That little "white lie" you told, that office stapler you took home, those salacious web sites you frequent—all of these fall under what the world might call "no big deal." But what we do in secret will eventually be exposed in ways we never anticipated, either in this life or before God. Whether that’s someone coming across your browsing history, learning of your lie, or realizing the stapler and other office supplies often disappear when you're working. "Small" sins here and there can lead to big exposure down the line.

But let's say they don't. Even if no one on Earth ever finds out, God sees and knows. He may allow us to make it through this life without embarrassment, but He will expose everything in the next life (Ecclesiastes 12:14). Worse still, if we never trusted in Christ as our Savior, after exposing our sin, we will be eternally punished in Hell for it (Revelation 20:15). Even if we are saved, the consequences of our sins are real and can be really painful both to us and to others.

So, right now, it may feel like you are getting away with your sin. But as Psalm 14, says, “The fool has said in his heart, ‘There is no God.’” Those who act like God doesn’t know or care about what they are doing are sorely mistaken. He will expose us for who we are. But the good news is that He has provided a way out of eternal punishment for our sin: Christ. Accepting Christ as Savior not only will provide abundant joy in this life but will also ensure that we are covered in His righteousness in the life to come.